What Do The Recent Rainfall Events Mean For The Highland Lakes?

I have been asked this question or some derivative quite a bit lately. Which makes since, considering we have had some notable rainfall events around the Austin Metroplex and central hill country area. In fact these two recent rainfalls are easily argued as the most significant events in the past 3 years (or specifically since Tropical Storm Hermine in September of 2010, which accounted for nearly 12 inches in some parts of Travis and Williamson counties). To keep this discussion concise, let’s just consider lake levels in Lake Travis, which has been the focal point of many water wows.

The short answer is the recent rainfall and flooding events have had some affect on the standing elevation of Lake Travis, but maybe not as much as one might expect in a purely mathematical sense. The lake’s level has been rising, a promising trend, since it had been steadily dropping for the past few years, however the recent increases in standing elevation from two significant rainfall events total up to less than 7 feet. At this writing Lake Travis sits at a head elevation of 624.89 feet, up from a low of approximately 618.5 feet in mid-September. Rainfalls in mid October did lead to a significant rise in flow in the Pedernales River, which is the largest tributary contributing to Lake Travis. However, the most recent rainfall event during the early morning of October 31st, was focused on south/southeastern Travis and Hays counties flooding parts of Austin and leading to Onion Creek bursting its banks and rising to levels never before seen. Onion Creek merges with the Lower Colorado River a few miles below Longhorn Dam and Lady Bird Lake. These flood waters are slowly making their way down to the coast. This most recent event will result in little if any significant change in the mean elevation of Lake Travis.

Current and historical stage and streamflow data for Texas river basins can be found at the USGS website. Current and historical lake levels and summary data for most of the streams and rivers in the Colorado basin are available from the LCRA website.

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